Another conspiracy theory claims Ruby may have been in a plot involving the CIA, which, among other Cold War-related reasons, disliked the fact Kennedy refused to assassinate Cuban communist dictator Fidel Castro.

This centres around an allegation that the nightclub boss told his erstwhile defence lawyer Tom Howard that mentioning the name “Davis” might harm his case.

It later emerged that Eli Davis III, as well as being known to Ruby as a gunrunner for anti-Castro Cuban rebels, was a CIA-connected mercenary.

Pallbearers are seen carrying the flag-draped casket of Jack Ruby in Chicago. (PA)

Yet no conclusive evidence supports any of these allegations and there has also been widespread criticism of these conspiracy.

Ruby told the Warren Commission, which was chaired by Chief Justice Earl Warren, that he was not part of any conspiracy to kill Kennedy.

He also reportedly revealed on his deathbed that he alone killed communist sympathiser Oswald because he was deeply upset about the president’s assassination.